This Program Project of 25 years brings together five Projects and three Cores from 2 institutions and 4 laboratories to explore the physiologic and pathophysiologic roles and signaling mechanisms of neuroendocrine peptides. Over the next period, we will continue our focus on receptors and ligands related to corticotropin releasing factor (CRF), a peptide we chemically identified at the inception of the Program. CRF is the principal neuroregulator of the hypothalamic-pituitary-adrenal (HPA) axis and acts within the brain to integrate endocrine, autonomic and behavioral responses to stress. Many human disorders including anorexia nervosa, anxiety, obesity, drug addiction and depression are associated with perturbations of the HPA axis and changes in sensitivity to CRF. In previous grant periods, we have chemically and biologically characterized multiple components of this system including two receptor genes, a soluble CRF binding and inactivating protein and the neuropeptide, urocortin (Ucn), which has high affinity for both receptor types. Over the past grant period we have identified two new neuropeptides, Ucn 2 and Ucn 3, both of which are highly selective for the second CRF receptor and both exert CRFR2-mediated effects on the endocrine, central nervous, gastrointestinal and cardiovascular systems. We have now developed mutants that are deficient in urocortins 1, 2 and 3. The brain and peripheral distribution and regulation of the two new urocortins are being studied along with their potential physiologic and pathophysiologic roles. The 3-dimensional structure of a major binding domain of CRFR2 has been solved by NMR and a native soluble protein encompassing that domain identified. New potent and selective peptide antagonists of CRFR1 and CRFR2 have been developed and are being used in acute studies to probe the physiologic significance and the pharmacologic promise of these important signaling systems. All of the Projects in this Program are testing hypotheses relating to CRF and Ucn, their regulation and physiologic importance and are taking advantage of recently characterized ligands and receptors, knockout mice, antibodies and improved and selective CRF receptor agonists and antagonists developed by various components within the Program, which are as follows: W. Vale, PD: CRF and urocortins and their receptors; J. Rivier, PD: Pharmacology of Neuroendocrine peptides;R. Riek, PD: Structural studies of the interaction between CRF G-protein coupled receptors and their ligands; G. Koob, PD: Behavioral significance of neuroendocrine peptides;P. Sawchenko, PD: Anatomy of neuroendocrine peptide pathways in the brain;Core A, W. Vale, CD: Administrative;Core B, K-F. Lee and W. Vale, CD's: Biology;Core C, J. Rivier and W. Fischer, CD's: Chemistry.